Process for cracking hydrocarbon oils



May 24, 1927 w. F. FARAGHER ET AL. 1629'908 PROCESS FOR CRACKINGHYDROCARBON OILS Filed Jan. l5. 1921 MW MN kuma,

Patented May V24, .1927.'j

UNITED 4STATES PATENT OFFICE.

'WARREN F. FARAGHEB, AND WILLIAM ARTHUR GRUSE, 0F PITTSBURGH,v'PIlITll-SYL- i vaina,

vaina, A CORPORATION or muxas.

ASSIGNORS T GULF BEFINING `CQMIPANYy OF PITTSBURGH, PENNSYL- PROCESS FORCRACKING HYDROCARBON OILS.

conduction of heat into the oil, and results in increased cost ofgasoline-production,

.towing to the necessity of cleaning the carbon from the still walls andthe loss of operating time during such cleaning operations; While thelife of the still wall is comparatively short due toI the rapid burningout ot' the iron in contact with carbon These diihculties areencountered in externally heated stills of various kinds, includingstills of the water-tube boiler type, where the oil is heated in itspassage through a series'of tubes. v

Attempts have been made to overcome the difficulties mentioned byproviding stirrers. in the still for agitation of the oil, and', in

stills of the water-tube boiler type, it has been'proposeol in oilcracking operations to provide mechanical stirrers or propellers forincreasing the circulation through the heated tubes (a practice wellknown in steam boiler operations) but such mechanical stirrers andpropellers are open to theiobjectionithat 1 they require stuffing boxeswhich must operate against highly heated oil and heated oil vaporsathigh pressures.

proved method for cracking oils in which -the cracking. operation' iscarrie out in a still of the water-tube boiler type,and in which apositive and efficient circulation of.

Vwithout mechanical agitators or propeller-s, and with avoidance orsubstantial avoidance vof .objectionabledeposition of carbon in .oilthrough the tubes isefected, according to the `present invention, by theintroduction of a jet or a series of jets of gas, or by the internalgeneration of gas, acting on the air-lift principle, to bring about arapid The present invention relates to-an imthe oil through theheatedtubes is effectedv the heated tubes. This circulation o f the andeffective circulation of the oil through the hea-ted tubes..

The gases used fory effecting the circulation of the oil, according tothe present invention, may with advantage be the fixed gases formedduring the cracking operation, or the mixed gases and vapors taken fromthe vapor line of the still and recirculated; but other appropriategases can be used, such as natural gas or casing-head gas, or othergaseous materials, such as steam, which have no objectionable effectupon the cracking operation. The introduction or reintroduction of thesegases into the stillhas the further advantage of promoting the'regularremoval of the lower boiling constituents resulting from the crackingoperation as they are formed, thus preventing their remaining in the'still to lundergo further objectionable cracking or decomposition. Whena portion of the gases or vapors produced by the cracking operation isrecirculated through the' still, these gases maybe freed from a part orthe whole of the readily condensible constituents before recirculation,oor the ho-t gases and vapors from the still can be recirculated withthe removal therefrom of only thehigher boiling constituents.

The invention will be further illustrated and described in connectionwith the accompanying drawings, which show, in a somewhat conventionaland diagrammatic manner, different forms of apparatus adapted' for thepractice of the process of the invention.

In the accompanying drawings,

Fig. 1 shows one form of apparatus em-- bodying the invention inverticallongitudinal section and with parts in elevation; and

' Fig. 2 is an end view of the apparatus of Fig. l, with the' furnacestructure' removed. In the apparatus illustrated, the still is of 'the`water-tube vboiler type and is made up of the upper longitudinal drum1,- the two lower transverse drums 2 and 4 with vertical connecting legsor tubes'3 :md5- respectively, and with 'a series of -tubes 6 connectingthe two lower transverse drums and suitably arranged to be heated in afurnace cham- .ber 7.

The u per longitudinal drum 1'has a suitable ephlegmator 8 and a vaporpipe 9 leading therefrom is supplied to the-upper drum from an oil- Athecondenser 17.- O11 'the suppl -vapor plpe 13 connects the vapor space ofthe oil supply tank 10 with the vapor pipe 9 so that the same pressurewill be maintained in the oil supply tank as in the still and so thatoil will automatically flow from tank to the still to maintain aconstant evel therein. An outlet for the residue is indicatedv at thebottom of the still at 15.

In the shorter depending legs 5 there are provided foot-pieces 14through which gas is introduced from pipes 16. The gas is blown inthrough thefoot-pieces 14 so as to cause a rapid and positive flow ofoil up through these legs. This, in turn, causes a rapid and effectivecirculation of oil through the heated tubes 6, the oil circulatingdownwardly through the leg .3 to the transverse drum 2, thence throughthe heated tubes to the drum 4 and upwardly through the legs 5, andbeing repeatedly recirculated in -this way. In this way the oil is kept`rapidly circulating-through thetubes 6 and deposition 0f carbon inthese tubes, which is the chief source of trouble in stills of thistype, is avoided or minimized. The tar and heavier sediment collect atthe bottomof the transverse drum 2 and are discharged through the outlet15.

The construction and arrangement, as well as the number, of the tubes,and of the depending legs, joining the upper longitudinal drum with. thetwo lower transverse drums, can be varied. AThe construction andarrangement should preferably be such as to give a substantially uniformdistribution and flow of the oil through the tubes.` This uniformity ofdistribution and of flow can be promoted, for example, by providing aplurality ofdepending legs, such?A as are shown at 5'. The provision ofa plurality of such legs, each with a gas inlet pipe for securing anair-lift action therein, permits the regulation of the flow through thetubes, to a greater or less extent, by-varying the gas introduced intothe different legs. For example, if an increased velocity of flow isproduced in the outer legs 5, this will tend to increase thepfiow of oilthrough the outer pipes, thus preventing-or reducing the tendency forthe oil to flow more slowly in the outer tubes than in the centrallyarranged tubes. i

In the operation of the apparatus and the carrying out of the oilcracking process, the

oil isheated by its passage through the .tubes 6 and pressure ismaintained in the still 4by placing a suitable regulating valve 18- inthe vapor line, preferably beyond the condenser as shown, therebyconfining the vapors and fixed gases developed by the process andmaintaining the proper pressure for the cracking operation. The oilinflow is supplied from the oil reservoir 10 in which the oil level ismaintained in any suitable manner, as by a pump controlled by anautomatic fioat device (not shown). There are no stuffing boxes ormoving parts of the still, but rapid and effective circulation of theoil through the heating tubes is nevertheless effected by theintroduction of gas in the manner described.

The operation is continuous and can be continued for long periods oftime, the residuum accumulating. and being removed through the outlet 15and the oil being automatically supplied to maintain a constant levelwithin the still. The rapid circula; tion of the oil within the stillpromotes uniformity of heating and of cracking, thusavoiding orminimizing local overheating. The continuous rapidcirculation of the oilthrough the heated tubes causes the oil in contact with the heated Wallsof the device to" be continuously swept or scoured off so that theformation of a dead layer of oil is prevented, with resulting preventionor substantial prevention of the heating oflsuch a layer toobjectionably high temperature.

It is one advantage of the invention that the use of moving mechanism isavoided, so that stuffing boxes are avoided, and so 'that allconnections of the stilhmay be welded and made gas-tight.

The introduction of a current or currents of gas not only serves toinsure effective agitation and circulation of the oil, but it promotesthe regular removal of the lower-boiling constituents resulting from thecracking operation as they are formed, and prevents their remaining inthe still to undergo further decomposition. The excess gas, resultingfrom the cracking operation, can be discharged from the still in any oflthe usual ways, while the gas that is to be recirculated through thestill can be freed from undesired high boiling constituents in asuitable dephlegmator, and from the desired condensible constitutents ina suitable condenser, and canv then be passed through a pump orgas-booster 19 and sufficiently increased in pressure to 'be used again.

By drawingy off the admixed fixed gases and vapors, from the vapor pipe9 atstill pressure and at substantially still temperature -throughconnection 20, and by recirculating and reintroducing .these gases forbringing about the circulation of the oil, the amount of work requiredfor compression of the gases is reduced and the sensible heat of thegases can be sufiiciently conserved s o that they exert no objectionablecooling effect when reintroduced.

In the apparatus illustrated the heated tubes are made slightly curvedso as to avoid strains set up by expansion and contraction.

The oil supply to the still may be preheated to a greater or lessextent, preferably to such a degree as to vaporize and remove any Waterpresent therein before the oil is supplied to the still. By preheatingthe oil in this way',` the preheating effect required from the tubeswill be correspondingly reduced. yA part of the heat necessary for thepreheating can be supplied by nieans of a neat interclianger throughwhich the still bottoms are discharged; while a part ot' the pieheatingmay be effected bybringing the oil into heat interclianging relationwith the hot vaporsfrom the still, for example, by passing the oilthrough the condenser for the vapors of distillation and cracking, orthrough one or more of the series. of condensers where such a series isused. The preheating effect thus secured may be supplemented, ifdesired. by further preheating of the oil in any suitable manner. Owingto the rapid and continuous circulation of the oil through the heatedtubes, uniformity of heating is promoted, and the resulting crackingoperation is of a inoie uniform chai'acter and results in an increasedyield of gasoline and lower gas and coke losses, and hence an increasedcapacity or increased yields for a given size still, as compared with astill which is not provided with means for effecting such circulation.

It will, of course, be understood that the manner of introducing thegases for bringing about and promoting the circulation can bevaried, forexample, the gas iets can be varied in number and arrangement, as Wellasin shape and location, provided only 'that they' serve as means for`eilecting the constant and substantially uniform circulation of the oilthrough the heated tubes'.

Iii illustrating the apparatus in the accompanying drawings, we haveomitted the heat insulation or lagging of the still, con= nec-tingpipes, etc. but it will be understood that, in practice, suitable heatinsulation will be provided 'to avoid objectionable losses I' from allexposed parts of the still and of the system which become heated.

It will be understood that the stills will,

l in practice, be provided with suitable "temperature, pressure andlevel indicating devices (not shown) as well as means for producing andmaintaining within the still the necessary temperature and pressureconditions. for .the cracking operation. -The cracking operation maythus be carried outl vundera'regulated pressure, for example, of

between 60 and 500 pounds persquare inch,

land preferably inthe neighborhood of 7 5. to

1.50 pounds per square inch, depensding upon the nature'ofv the oil tobe crack'ed and the products desired. v

In referring to the cracking of oil in the. present specification andclaims, we in,-l tend to include the treatment of various'hy'-vdrocarbon oils, and more particularly the;`

treatment of higher' boilingfractions and' residual oils of petroleum orshale oil distillation, for the vproduction of motor fuel or cation maybe arranged in series and the oil to be cracked passed through themconsecutively. v

We claim: l. The method- 0f cracking oils in a pressure still, whichcomprises maintainingA a pool of oil and circulating oil from the pooldownwardly to one end of `heating tubes,-

thence through the heating tubes,'and upwardly back from the other endof the heating tubes to the said pool, heating the oil to a crackingtemperature in the said heating tubes, and promoting circulation of theoil vthrough the heating tubes by introducing a current or currents ofgas, acting on the air-lift principle, into the oil at a point .in

its passageupwardly between the heating` tubes and said pool.

2. The method of cracking oils in a pressure still, which comprisescirculating the oil from and to-a drum through tubes heated to alcracking temperature and promoting the circulation of oil through theheated tubes of the still by introducing current or currents of gas,acting on the air-lift principle, into the oil at a point in its passageupwardly between the tubes and the drum.

3. The method of cracking oils in a pressure still, which comprisescirculating the oil from and to a drum through tubes heated to acracking temperature and promotin the circulation of. oil through thelieate tubes of the still by`introducing a current or currents of gasfrom the still', acting on .the air-lift principle, into the oil at apoint in its passage upwardly between the tubes s' and the drum.

4. The method of cracking oils in a pressure still, which comprisesvcirculating the oil from and to a drum through tubes heated to acracking temperature and promoting the circulation of oilthrough theheate tubes of the still by introducing arurrent or currents of gas andvapor from the still and at substantially thestill temperature,

acting on'the air-lift principle, into thev oil at a point infits.passage upwardly bef,

tween the tubes and the. drum. l

5. The process of -pyrogenetically distilling lower boiling pointhydrocarbon oils from higher boiling point hydrocarbons which consistsin maintaining a bulk supply thereof under pressure, withdrawing oiltherefrom, passing it in a stream through a heated zone and returning itto said bulk supply, and injeeting u gaseous medium into it in thedirection of its iow in its passage between the heated zone und the bulksup- Plyl 6. The process of pyrogenetloully distilling lower boilingpoint hydrocarbon oils from higher boiling point hydrocarbons whichconsists in maintaining a bulk supply thereof under pressure,withdrawing oil therefrom, passing it in an upwardly directed streamthru a heated zone and back to the bulk supply, whereby circulation ofthe oil is thermally maintained, and injecting steam upwardly into theoil in its pas-- sage between the heated zone and the bulk supply.

ln testimony whereof We affix our signa- 20v tures.

WARREN F. FARAGHER. WILLIAM ARTHUR GRUSE.

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